1. Field of the Invention
This invention relates to polymer compositions and especially to electrically conductive compositions.
2. Introduction to the Invention
Electrically conductive adhesives are employed in a number of fields where good electrical continuity is required. For example, when a shielded electrical cable is terminated with an electrical connector, a screened enclosure, e.g.: in the form of a dimensionally recoverable article, may be located over the connector and cable to provide a continuous screening between the connector and the cable shield. Such articles are described in U.S. Pat. No. 4,467,002, the disclosure of which is incorporated herein by reference. It is important to maintain a good electrical connection between the screen and the enclosure and both the connector and the cable shield, and electrically conductive adhesives have been employed for this purpose.
Electrically conductive adhesives can be formed by blending a quantity of electrically conductive material, e.g. a metal, into a solutions of the adhesive in a suitable solvent and evaporating the solvent. Normally silver flake is employed for this purpose in view of the relatively low bulk resistivities that can be achieved. The bulk resistivity of the adhesive will fall sharply with the increase in volume loading of metal until a so-called "percolation threshold" is reached after which the resistivity is low and relatively constant with respect to the metal loading. The silver loading employed will depend on the type of adhesive, but loadings in the region of 12-15% by volume may be used, may be used.